1. Field of the Invention
The present invention relates to a semiconductor transducer and to its use in a sensor for detecting electron-donor or electron-acceptor species.
2. Description of Related Art
Various devices for detecting gaseous molecules, especially those comprising a semiconductor transducer of the resistor, transistor or diode type, are known.
There are many types of diodes having various types of semiconductor materials, a few examples of which have been used as chemical sensors. In particular, R. Dobulans, J. Latvels, I. Muzikante, E. Fonavs, A. Tokmakov and M. Bouvet [“Molecular diode for gas sensing”, Proceedings of the NENAMAT Mobilization Workshop “Nanomaterials and Nanotechnologies”, 30-31 March, Riga, 2005, 130] discloses a diode in which the two semiconductor layers are formed by two different molecular materials, of type p and type n respectively. However, the geometry and the operation of this device are not optimized for its use as a chemical sensor, and its forming operation is complex.
M. Bouvet and A. Pauly [Encyclopedia of Sensors, Editors C. A. Grimes, E. C. Dickey and M. V. Pishko, Vol. 6, pp. 227-269] describe transducers of the resistor type or of the field-effect transistor type, in which the sensitive element is an electroactive molecular material. Such materials are described in particular by J. Simon, J.-J. André and A. Skoulios [“Molecular Materials. I: Generalities”, Nouv. J. Chim., 1986, 10, 295-311] and by J. Simon and P. Bassoul [“Design of Molecular Materials”, Wiley, Chichester, 2000].
A field-effect transistor is formed by the following succession of layers: a conducting substrate (for example doped Si); an insulating layer (for example SiO2 or Si3N4); and a layer of a metal monophthalocyanine (MPc). The MPc layer is connected to a source electrode and to a drain electrode, and the conducting substrate is connected to a gate electrode. The MPc layer constitutes both the sensitive layer and the material in which the measured current flows, said current being modulated by the voltage applied to the gate electrode. The molecular material may be a semiconductor polymer, phthalocyanine (substituted or unsubstituted), a porphyrin (substituted or unsubstituted), an oligothiophene (substituted or unsubstituted), a pentacene, a fullerene or a perylene derivative. Such a device performs well for detecting molecules. However, its production involves complicated technological steps.
A gas detector of the resistor type comprises, for example, an alumina substrate on one of the faces of which two interdigitated Pt electrodes are placed, on the top of which a film of copper phthalocyanine (CuPc) is deposited. The other face of the substrate comprises Pt resistors for heating the substrate. The conductivity of the CuPc increases with the O3 content or NO2 content of a gas mixture with which the CuPc is in contact. The drawback of such a device lies firstly in the absence of selectivity relative to the gas molecules to be detected, and secondly its performance limitation.